The present invention relates to hybrid powertrains, for example for automobiles, passenger vehicles, buses, trucks, boats and stationary applications. Moreover, the invention also concerns methods of controlling such powertrains, for example with regard to combustion engine cranking and gear change. Furthermore, the present invention also relates to vehicles, boats and similar including such powertrains. Additionally, the present invention relates to software executable on computing hardware for executing the methods of controlling such powertrains.
In recent years, considerable research has been invested in hybrid system technology in order to provide enhanced fuel economy as well as improved motive performance. Hybrid systems include hybrid powertrains, wherein each powertrain usually comprises a combustion engine, an electric machine arrangement, an electrical storage element, a control unit for managing the powertrain, and a transmission arrangement for coupling at least the electric machine to a load of the system. The electric machine is optionally implemented as a motor/generator. Superficially, such hybrid powertrains would seem to involve additional complexity and potentially added weight which would be deleterious to system performance. However, in practice, several benefits arise from employing hybrid powertrains in comparison to conventional simple combustion engine systems which operate sub-optimally, especially in urban stop-start scenarios.
In contemporary hybrid powertrains, enhanced energy economy can be obtained by operating a combustion engine at its most thermally efficient range and periodically stopping and starting the combustion engine. When the combustion engine is not in operation, motive power is provided by one or more electric motors coupled to a rechargeable battery via electronic control circuits. When the combustion engine is in operation, the combustion engine can be recharging the rechargeable battery and/or providing motive power. Moreover, in some designs of hybrid powertrain, the one or more electric motors can be configured to function as generators for providing regenerative braking wherein kinetic energy is converted at braking to recharge rechargeable batteries.
A technical problem encountered in practice is that drivers of contemporary simpler combustion engine vehicles are accustomed to refined performance wherein their vehicles perform quietly without greatly perceptible vibration from their engines. In contradistinction, hybrid vehicles designed so that their combustion engines intermittently are activated and deactivated can be prone to additional vibration and abrupt changes in available motive torque which drivers experience as disconcerting and potentially dangerous when attempting critical maneuvers, for example overtaking another vehicle.
This technical problem has been previously appreciated and is addressed in a hybrid powertrain described in a published U.S. Pat. No. 4,533,011. In overview, there is described a powertrain as illustrated in FIG. 1. The powertrain is indicated generally by 10 and comprises an internal combustion engine 20 including an exhaust manifold 30. The combustion engine 20 is coupled to a fuel supply controlling device 40 configured to be supplied with fuel from a fuel tank 50. An output crank shaft of the combustion engine 20 is coupled via a first disconnecting clutch 60 to an electric machine 70 operable to function both as an electric motor and an electric generator. The electric machine 70 is further coupled via a second disconnecting clutch 80 to an input of a gear transmission 90; the transmission 90 is operable to provide geared transmission whose gearing ratio is controlled via a gear control unit 100. An output of the transmission 90 is connected via a differential gear 110 to wheels 120 of a vehicle accommodating the powertrain 10.
The powertrain 10 in FIG. 1 further includes a rechargeable battery 200 coupled via an electronic control unit 210 to the electric machine 70; the electronic control unit 210 is operable to control electrical power supplied to the electric machine 70 to generate torque therein, and to control electric energy generated within the electric machine 70 which is coupled to the rechargeable battery 200 for recharging the battery 200. The powertrain 10 further comprises an engine management control unit 220 which is coupled in communication with the disconnection clutches 60, 80, with the electronic control unit 210 and with the fuel supply controlling device 40.
Operation of the powertrain 10 will now be described in overview. The electric machine 70 is designed to function as a flywheel for the combustion engine 20 so that the combustion engine 20 is less massive and has less rotational inertia associated therewith when decoupled by the first clutch 60 from the electric machine 70. When the second clutch 80 is decoupled and the first clutch 60 is coupled, the electric machine 70 is operable to crank the combustion engine 20 to start the combustion engine 20 into operation by supplying fuel thereto via the supply controlling device 40. When the combustion engine 20 is activated and operational, the second clutch 80 is then engaged to couple motive power generated by the combustion engine 20 and optionally the electric machine 70 via the transmission 90 to the one or more wheels 120 to propel the powertrain 10 and its associated vehicle. When the combustion engine 20 is subsequently to be deactivated, the first clutch 60 is disengaged and the fuel supply controlling device 40 then interrupts supply of fuel to the engine 20. On account of the combustion engine 20 being isolated by way of the first clutch 60 being disengaged, minimal vibration and substantially no sudden changes in available torque are experienced by a driver of the vehicle accommodating the powertrain 10.
When driving away from a stationary state, the first clutch 60 is substantially disengaged and the electric machine 70 is employed for generating an initial substantial starting torque so as to provide a smooth and rapid acceleration of the vehicle. When the vehicle has attained a threshold speed, the first clutch 60 is then engaged so that torque provided by the combustion engine 20 can be used to supplement that provided from the electric machine 70. When the combustion engine 20 is deactivated, torque for propelling the vehicle is provided solely by the electric machine 70.
Although the powertrain 10 illustrated in FIG. 1 provides many technical advantages in operation, it nevertheless represents a complex configuration with the two clutches 60, 80. Moreover, even though the combustion engine 20 relies on the electric machine 70 to function as a flywheel, the combustion engine 20 when still rotating and decoupled from the electric machine 70 is potentially prone to unstable operation before coming to a rotational standstill on interruption of its fuel supply.
Thus, the powertrain 10 does not represent an optimal powertrain configuration and is susceptible to being further improved to simplify its implementation and provide yet further improved vibration and smooth torque generation characteristics.
In a published U.S. Pat. No. 5,755,302, there is described a drive apparatus for a hybrid vehicle. The drive apparatus includes an internal combustion engine and a gear-shifting transmission unit. Moreover, the drive apparatus includes a rotatable crank shaft operatively connectable to the internal combustion engine, and a rotatable transmission shaft operatively connectable to the gear-shifting transmission unit. Furthermore, the drive apparatus further comprises a movable annular rotor disposed annularly about the transmission shaft, the rotor including a permanent magnet for generating a magnetic field and an attachment mechanism for attaching the rotor to the transmission shaft so that torque is transmitted in operation between the rotor and the transmission shaft. A stationary annular stator is attachable to at least one of the internal combustion engine and the gear-shifting transmission unit and is disposed concentrically about and proximate the rotor in an electromagnetically interactive relation. The stator includes a conductive winding for electromagnetically interacting with the magnetic field of the rotor.
Additionally, the drive apparatus includes only one clutch disposed at least partially within a recess of the stator, the clutch including two coupling mechanisms for selectively and frictionally coupling the crank shaft to the transmission shaft for torque transmission therebetween so that the clutch is switchable between: (a) an engaged position in which torque is transmitted between the crankshaft and the transmission shaft; and (b) a disengaged position in which the torque transmission between the crankshaft and the transmission shaft can be discontinued. An electronic control unit of the drive apparatus is operable to vary an electric load or torque generated by an electric machine comprising the aforesaid rotor and stator in a timely manner such that torque fluctuations at the transmission shaft are reduced by way of torsional vibration damping. In so doing, frictional engagement can be achieved sufficiently smoothly so that engagement of the clutch is free of jolts and induces minimal wear. The transmission is braked electrically by the electric machine in order to shift up a gear, and is accelerated electrically to shift down a gear. However, such synchronization for gear change takes time to implement in operation.
It is desirable to provide an improved hybrid powertrain.
According to a first aspect of the invention, there is provided a hybrid powertrain including:
a combustion engine;
an electric machine arrangement;
a gearbox operable to receive motive power from at least one of the combustion engine and the electric machine arrangement for providing corresponding motive power to a load;
a control unit coupled in communication with the combustion engine, the electric machine arrangement and the gearbox for controlling their operation;
wherein the powertrain is configurable in operation so that its combustion engine is switchable between an inactive state and an active state, the combustion engine requiring to be cranked to switch it from its inactive state to its active state,
characterized in that
the control unit includes multiple-inputs for receiving feedback signals derived from the powertrain and command signals to the powertrain, and multiple-outputs for outputting output signals for controlling operation of the powertrain; and
the control unit further includes computing hardware operable to execute a torque simulation of the powertrain, the simulation being applicable in operation to process information provided at the multiple-inputs to compute a compensation, the control unit being operable to apply the compensation at the multiple outputs to reduce an amplitude of torque jerks occurring in operation in the powertrain when the engine is switched between its active and inactive states.
The invention is of advantage in that powertrain is capable of providing improved performance with regard to reduced sudden torque variations, namely “jerks”, as well as with regard to simplicity and ease of operation.
Optionally, in the hybrid powertrain, application of cranking torque to the combustion engine is controlled in operation by the control unit to substantially temporally coincide with a gear change in the gearbox.
Beneficially, in the powertrain, wherein, whilst the gearbox is in a neutral coupling state, the combustion engine is operable to be cranked by decelerating the electric machine arrangement to substantially a standstill, at least partially rotationally coupling via a rotational coupling arrangement the combustion engine to the electric machine arrangement applying excitation to the electric machine arrangement to rotationally accelerate it and thereby accelerating the combustion engine to a threshold rotation rate, and then applying a fuel supply to the combustion engine to bring the combustion engine to an active state. Such an approach is capable of reducing wear of the coupling arrangement and is also potentially highly energy efficient with regard to recovering energy to recharge the energy storage element before commencing cranking of the combustion engine.
Optionally, in the powertrain, wherein, whilst the gearbox is in a neutral coupling state, the combustion engine is operable to be cranked by maintaining the electric machine arrangement in a rotating state, at least partially coupling via a rotational coupling arrangement the combustion engine to the electric machine arrangement to transfer torque therefrom to the combustion engine, thereby accelerating the combustion engine to a threshold rotation rate, and then applying a fuel supply to the combustion engine to bring the combustion engine to an active state. Such an approach is potentially more rapid than decelerating the electric motor to substantially a standstill, but potentially may cause more wear of the rotational coupling arrangement.
Preferably, in the powertrain, the rotational coupling arrangement includes a slipping clutch operable to provide a constant-torque coupling characteristic through at least part of its slippage range. Such a constant-torque characteristic is effective at filtering sudden torque variations, namely “jerks”.
Preferably, in the powertrain, the electric machine arrangement is coupled via a series arrangement of the clutch and a rotationally-compliant torque coupling to the combustion engine.
Preferably, in the powertrain, the rotational coupling arrangement includes a clutch couplable between the combustion engine and the electric machine arrangement. Such a configuration is found in practice to be compact, simple and robust.
Preferably, in the powertrain, one or more rotational shafts of the combustion engine and the electric machine arrangement are provided with one or more sensors coupled to the control unit for determining a measure of torque coupled to the combustion engine when cranking the combustion engine and causing it to be activated, such measure of torque being processed by the control unit for providing control of the electric machine arrangement for at least partially compensating any abrupt changes in torque occurring in the powertrain. Use of the measure of torque is capable of enabling the control arrangement to more finely control the powertrain to avoid occurrence of “jerks” therein when activating the combustion engine.
Preferably, in the powertrain, the one or more sensors are implemented as rotation rate sensors for measuring rotation rate of their one or more shafts, the measure of torque being computed by the control arrangement from inertial moments of components parts of the powertrain and from angular acceleration temporally computed from the one or more measured rotation rates.
According to a second aspect of the invention, there is provided a hybrid powertrain including:
a combustion engine;
an electric machine arrangement;
a gearbox operable to receive rotational power from at least one of the combustion engine and the electric machine arrangement, the gearbox being operable to provide motive power to a load;
a control unit coupled in communication with the combustion engine, the electric machine arrangement and the gearbox for controlling their operation;
wherein the powertrain is configurable in operation so that its combustion engine is switchable between an inactive state and an active state, the combustion engine requiring to be cranked to switch it from its inactive state to its active state;
characterized in that
application of cranking torque to the combustion engine is controlled in operation to substantially temporally coincide with the gearbox being engaged to couple motive power to the load of the powertrain; and
wherein one or more of rotational shafts of the combustion engine and the electric machine arrangement are provided with one or more sensors for determining a measure of torque coupled to the combustion engine when cranking the combustion engine and causing it to be activated, such measure of torque being processed using a torque simulation of the powertrain executed in operation on computing hardware of the control unit for providing control of the electric machine arrangement for at least partially compensating any abrupt changes in torque occurring in the powertrain.
Such a configuration for the powertrain is of benefit in that motive power is maintained to propel the vehicle simultaneously with the combustion engine of the vehicle being activated.
Optionally, in the powertrain, whilst the gearbox is in an engaged coupling state, the combustion engine is operable to be cranked by maintaining the electric machine arrangement in a rotating state, at least partially coupling via the rotational coupling arrangement the combustion engine to the electric machine arrangement to transfer torque from the electric machine arrangement to the combustion engine, thereby accelerating the combustion engine to a threshold rotation rate, and then applying a fuel supply to the combustion engine to bring the combustion engine to an active state.
Optionally, in the powertrain, the one or more sensors are implemented as rotation rate sensors for measuring rotation rate of their one or more rotational shafts, the measure of torque being computed from inertia) moments of components parts of the powertrain and from angular acceleration temporally computed from the one or more measured rotation rates.
According to a third aspect of the present invention, there is provided a method of controlling a hybrid powertrain including:
a combustion engine;
an electric machine arrangement;
a gearbox operable to receive rotational power from one or more of the combustion engine and the electric machine arrangement, and to provide motive power to a load;
a control unit coupled in communication with the combustion engine, the electric machine arrangement and the gearbox for controlling their operation; and
wherein the powertrain is configurable in operation so that its combustion engine is switchable between an inactive state and an active state, the combustion engine requiring to be cranked to switch it from its inactive state to its active state,
characterized in that the method includes steps of:
receiving feedback signals derived from the powertrain and command signals at multiple-inputs of the control unit, and outputting output signals at multiple-outputs of the control unit for controlling operation of the powertrain; and
applying at the control unit a torque simulation of the powertrain executable on computing hardware of the control unit, the simulation being applicable in operation to process information provided at the multiple-inputs to compute a compensation, the control unit being operable to apply the compensation at the multiple outputs to reduce an amplitude of torque jerks occurring in operation in the powertrain when the engine is switched between its active and inactive states.
Optionally, the method includes steps of:
(a) initiating a gear change by reducing torque supplied to the gearbox and then placing the gearbox in its neutral state;
(b) controlling application of cranking torque to the combustion engine to substantially temporally coincide with the gearbox being in the neutral state, the cranking torque and supply of fuel to the combustion engine being operable to cause the combustion engine to be activated; and
(c) engaging the gearbox into gear and then increasing torque supplied to the gearbox.
Optionally, the method includes additional steps of:
(d) whilst the gearbox is in a neutral coupling state, cranking the combustion engine by decelerating the electric machine arrangement to substantially a standstill;
(e) at least partially coupling via a rotational coupling arrangement the combustion engine to the electric machine arrangement,
(f) applying excitation to the electric machine arrangement to rotationally accelerate the electric machine arrangement and thereby accelerating the combustion engine to a threshold rotation rate; and then
(g) applying a fuel supply to the combustion engine to bring the combustion engine to an active state.
Optionally, the method includes additional steps of: (h) whilst the gearbox is in a neutral coupling state, cranking the combustion engine by maintaining the electric machine arrangement in a rotating state;
(i) at least partially coupling via the rotational coupling arrangement the combustion engine to the electric machine arrangement to transfer torque from the electric machine arrangement to the combustion engine thereby accelerating the combustion engine to a threshold rotation rate; and then
(j) applying a fuel supply to the combustion engine to bring the combustion engine to an active state.
Optionally, in the method, the coupling arrangement includes a slipping clutch operable to provide a constant-torque coupling characteristic through at least part of its slippage range.
According to a fourth aspect of the invention, there is provided a vehicle including a hybrid powertrain according to the first or second aspect of the invention.
Preferably, the vehicle is selected from a group: a bus, a truck, a construction vehicle, a van, a passenger vehicle, a boat, a ship, a stationary machine, or any type of vehicle which is required in operation to exhibit relatively high acceleration in a stop-start manner of driving.
According to a fifth aspect of the invention, there is provided a method of controlling a hybrid powertrain including:
a combustion engine;
an electric machine arrangement;
a gearbox for receiving rotational power from at least one of the combustion engine and the electric machine arrangement, and for providing motive power to a load;
a control unit coupled in communication with the combustion engine, the electric machine arrangement and the gearbox for controlling their operation; and
wherein the powertrain is configurable in operation so that its combustion engine is switchable between an inactive state and an active state, said combustion engine requiring to be cranked to switch it from its inactive state to its active state,
the method including steps of:
(a) engaging the gearbox into gear for coupling torque therethrough to provide motive power to the load;
(b) applying a cranking torque to the combustion engine and coupling a supply of fuel thereto to activate the combustion engine, such activation of the combustion engine coinciding substantially temporally with the gearbox being engaged; and
(c) wherein one or more of rotational shafts of the combustion engine and electric machine arrangement are provided with one or more sensors for determining a measure of torque coupled to the combustion engine when cranking the combustion engine and causing it to be activated, such measure of torque being processed in the control unit using a torque simulation model for providing control of the electric machine arrangement for at least partially compensating any abrupt changes in torque occurring in the powertrain.
Optionally, the method includes additional steps of:
(d) whilst the gearbox is in an engaged coupling state, cranking the combustion engine by maintaining the electric machine arrangement in a rotating state;
(e) at least partially coupling via a rotational coupling arrangement the combustion engine to the electric machine arrangement for transferring torque from the electric machine arrangement to the combustion engine thereby accelerating the combustion engine to a threshold rotation rate; and then
(f) applying a fuel supply to the combustion engine to bring the combustion engine to an active state.
Optionally, in the method, the one or more sensors are implemented as rotation rate sensors for measuring rotation rate of their one or more shafts, the measure of torque being computed by a control unit from inertial moments of components parts of the powertrain and from angular acceleration temporally computed from the one or more measured rotation rates.
According to a sixth aspect of the invention, there is provided a computer program on a data carrier, the computer program being executable on computing hardware for implementing a method according to the fourth or fifth aspect of the invention.
According to a seventh aspect of the invention, there is provided a computer program comprising computer program code means adapted to perform a method or for use in a method according to the fourth and fifth aspects of the invention when the computer program is run on a programmable microcomputer.
Preferably, the computer program is adapted to be downloaded to a powertrain according to the first or second aspect of the invention, or one or more of its components when run on a computer which is connected to the Internet.
Preferably, the computer program product is stored on a computer readable medium, comprising the aforesaid computer program code means.
According to an eighth aspect of the invention, the method for controlling a hybrid powertrain having a combustion engine, an electric machine arrangement and a gearbox operable to receive motive power from at least one of the combustion engine and the electric machine arrangement for providing corresponding motive power to a load; comprising the following steps starting from a powertrain operational state where the load is powered by means of the electric machine arrangement:
reducing an output rotational torque of the electric machine arrangement to the gearbox,
controlling the gearbox, and
cranking the combustion engine by means of the electric machine arrangement.
The method results in a powertrain operational state where the load is powered at least by means of the combustion engine.
The method is especially suitable for an acceleration procedure for a powertrain comprising a single clutch, wherein the electric machine arrangement is operationally arranged between the combustion engine and the gearbox and the single clutch is arranged between the combustion engine and the electric machine arrangement. Thus, the method creates conditions for eliminating a second clutch, which is present in many prior art solutions.
Further, the output rotational torque of the electric machine arrangement is preferably reduced to zero before the gearbox is controlled. The reduction procedure may be stepwise, ie substantially instant reduction, but the output rotational torque is preferably ramped down, ie in a gradual, continuous manner.
Further, the method steps are not necessarily performed in chronological order.
Preferably, the method comprises the steps of
shifting the gearbox to a neutral state after the reduction of the output rotational torque of the electric machine arrangement,
engaging a gear in the gearbox after shifting the gearbox to the neutral state, —ramping up an output rotational torque to the gearbox after the engagement of the gear in the gearbox,
ramping up the output rotational torque to the gearbox by means of ramping up at least the output rotational torque of the combustion engine (which is performed by injecting fuel to the engine), and
initiating injecting fuel to the engine at a predetermined speed of the engine.
The ramping up phase may be performed with a contribution of power from the electric machine arrangement.
Preferably, the method comprises the further step of synchronizing the output speed of the combustion engine before the output rotational torque of the combustion engine is ramped up.
Preferably, the method comprises the step of activating a coupling arrangement arranged between the combustion engine and the electric machine arrangement in order to crank the combustion engine by means of the electric machine arrangement. This may be performed in a plurality of ways; According to a first example, the method comprises the step of maintaining a specific rotational speed of the electric machine arrangement while simultaneously partially closing the coupling arrangement. According to a second example, the method comprises the step of decelerating the rotational speed of the electric machine arrangement to a standstill and totally closing the coupling arrangement before cranking the combustion engine by means of the electric machine arrangement.
Preferably, the method comprises the synchronizing step of detecting an output speed of the electric machine arrangement and an output speed of the combustion engine and totally closing the coupling arrangement when the detected output speed of the electric machine arrangement and the detected output speed of the combustion engine are within a predetermined speed range.
Preferably, the method comprises the step of adding an additional torque to the electric machine arrangement in order to compensate for the torque needed to crank the combustion engine. Preferably, the method comprises the step of detecting a plurality of powertrain operational parameters indicative of torque and calculating a magnitude of the additional torque on the basis of the detected powertrain operational parameters.
Preferably, the method comprises the step of cranking the combustion engine by means of the electric machine arrangement while the gearbox is in the neutral state.
Preferably, the method comprises the step of the step of cranking the combustion engine by means of the electric machine arrangement while the gearbox is in an engaged state. In this way, the total time for the procedure for starting the combustion engine and outputting torque from the engine to the gearbox may be shortened. Thus, the combustion engine is preferably cranked by means of the electric machine arrangement while an input shaft of the gearbox is engaged to the load. In this context, the method preferably comprises the step of cranking the combustion engine by means of the electric machine arrangement during the reduction of the output rotational torque of the electric machine arrangement to the gearbox or, alternatively during the ramping up of the output rotational torque to the gearbox.
In the last phase of the ramping down, there is available torque in the electric machine (ie the electric machine is not operating at its maximum or close to its maximum output rotational torque), and at least part of this available torque may be added at this stage. Similarly, in the initial phase of the ramping up there is available torque in the electric machine (ie the electric machine is not operating at its maximum or close to its maximum output rotational torque), and at least part of this available torque may be added at this stage. Thus, at both instances, there is available further torque in the electric machine, which may be used to crank the engine. Thus, during one of the defined parts of the ramp-up or ramp-down phase, the output torque of the electric machine arrangement is substantially increased (preferably to maximum output) for a short time interval in order to crank the engine.
Preferably, the method comprises the step of cranking the combustion engine by means of the electric machine arrangement after the synchronization of the output rotational torque of the combustion engine.
Preferably, the method comprises the step of cranking the combustion engine by means of the electric machine arrangement when the electric machine arrangement is in an operational state that differs substantially from an operational state in which the electric machine is operated at maximum output rotational torque.
Preferably, the method comprises the step of shifting gears in the gearbox (500) during said switching from powering the load by means of the electric machine arrangement to powering the load by means of the combustion engine.
It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as defined by the accompanying claims.